Wiring a PTO driven 21Kva 3-Phase Generator

[Darkness]

Many moons ago my father bought a pto driven 21kva 3-phase generator for use on a dairy farm. Anyhow, we had an electrician out to do a job and asked him to wire it if he had time. He quickly stuck a 3 pin socket on it as thats all he had.

Anyhow, that has done the job well but at the end of the day we are stuck with a 13a max load and as things has been upgraded such as coolers etc, the power demands of these coolers alone requires a bigger load demand especially when the motorss kick in.

What alterations should one get made to the generator to allow for the full potential of the generators ouput?

Can I get a connection point fitted say at the consumer unit to power all circuits on the cu especially the one thats for the milking parlor/coolers.

Cheers for any input as I need to get alterations made before the winter really kicks in and the generator is called for.

 

[flameport]

Assuming you have a 3 phase consumer unit:

Suitably rated 3 phase socket on the generator
3 phase inlet plug and changeover switch at the consumer unit.
Heavy duty cable/flex with plug on one end and socket at the other.
Earthing arrangements to be amended if required.

If only a single phase consumer unit, you will be stuck with only using a fraction of the generator capacity, unless you replace the consumer unit.

 

[ericmark]

Much also depends on the generator. Some have 12 windings allowing many configs including zig zag wirings which allows you to nearly get full output single phase from a three phase machine and more important balanced.

If not zig zag wired then 13A single phase is about your limit and you need to use it as a three phase machine.

Again a lot depends on the AVR type and without a lot more details hard to say exactly what it can do.

Although tractors are quite stable on revs you will get some droop and as the power goes up you need to consider how the things you are running will work when voltage and frequency are not spot on?

 

[Darkness]

View media item 16150
I hope the pic gives a better understanding of my generator even though it needs a good blowout.

We are single phase so the use of 3phase is of no benefit unless I had it wired with single and 3-phase sockets. If I am limited with single phase, what would be the maximum wattage that I could get out of the generator?

The way we operate it at the minute is we up the rev of the tractor till the voltage reaches 230 or so. If we wanted 400v for example, we would rev the tractor even higher.[/img]

 

[Aragorn84]

View media item 16150The way we operate it at the minute is we up the rev of the tractor till the voltage reaches 230 or so. If we wanted 400v for example, we would rev the tractor even higher.[/img]

That sounds a big dodgy to me?

Usually the voltage out of these things is regulated and the frequency ends up fluctuating slightly as the load changes.

With yours, surely the frequency changes as well as the voltage as the generator RPM's increase?

 

[Darkness]

The voltage does change on tractor rpm but with a decent tractor, the load used doesn't really alter the rpm unless you are playing with the arc welder when you would hear a change in tractor note.

When my father bought this generator, it was part of a huge grant type thing involving our electricity supplier. I was working abroad at the time but I first thought these things would come fitted with plugs and maybe breakers etc but no they didn't. You had to get them wired and a frame made to suit hold it.

This is one of the reasons why I need to know whats required so its meant to be in the state its meant to be in.

Anyhow, its done a great job all the same with a 3-pin plug.

 

[Aragorn84]

My point is more that you connecting it up to no doubt expensive farm machinery, and if its not regulating its output voltage correctly and the output frequency is at 69.4Hz instead of 50, then "Bad Things" could quite easily happen to all that expensive kit...

Its my understanding that a generator like that should have some sort of governor linkage to hold the engine at the RPM required to turn the generator at 50Hz. There will still be some fluctuation in the RPM as you apply and remove loads, but at least theres something trying to keep it fixed at 50hz. If you apply a huge load, the governor will pull the throttle open, and similarly when the load goes offline it will shut the throttle back.

Then the output voltage should be regulated down to the appropriate voltage for the supply.

If the RPM is under manual control via a hand throttle, then i cant see how the engine output can be increase to match the load, you set it to "230v" with the hand throttle and then fire up 10KW's worth of refrigerators, the engine is going to slow down, altering both the voltage and the frequency output.

 

[stunlawless]

The "throttle" on a diesel engine (hand or foot operated) is a device that sets the engine speed to which the governor (incorporated in the Fuel Injection Pump (FIP)) will attempt to control.

So, if you use the hand throttle to set the engine to 1500rpm with the genny off load, then when you start the milking pump, the governor will move the rack in in the FIP to increase the amount of fuel injected to match the load. You will hear the engine noise change (and maybe see more smoke up the stack), but the engine speed shouldn't change.

In the real world, there will always be a slight under & overshoot, as the governor is a very simple device that responds to an error in rpm. The magnitude of this under & overshhot will depend on how fast the extra load is applied and the characteristic of the governor.

IIRC 1500 rpm = 50Hz; 1800 rpm = 60Hz, and above a minimum speed (1200rpm ?) the voltage is constant, until the genny is overloaded.

Hope this helps, David

 

[Aragorn84]

I guess it depends on the injector pump.

The "throttle" on a standard Bosch VE pump as you find fitted to most older cars/vans etc (ie pre common rail) doesnt really work the way you described. Infact its almost the complete opposite.

On those pumps the "throttle" sets how much fuel the pump injects, and the governor is fixed, usually somewhere around 4500rpm for car engines.

Imagine sitting in your car driving along at 30mph. Now fix the throttle position, and start driving up a very steep hill. The engine would slow down, and possibly even stall. What you suggested though is that the FIP would start injecting more fuel to maintain the RPM's, which clearly doesnt happen.

If you pull the throttle say half open on an unloaded engine, it would wind itself round to the governor and sit there. As the rpm's approach the governed speed the pump cuts the fuel back. Apply a load thats going to draw 100hp from the engine without moving the throttle though, and the revs WILL drop to the point where the injected quantity of fuel manages to spin the load to.

Most PTO systems will have a seperate device, which works somewhat as you describe though. The engine still has a normal injector pump like above, but the PTO gear monitors the shaft speed and then opens or closes the throttle to maintain the target RPM.

Given that the OP is talking about adjusting the engine speed manually though, makes me wonder if this is actually present.

 

[stunlawless]

Aragorn, common (usual ?) to fit all-speed governer on agricultural & industrial engines, which operate as I described. I think what you describe is for road going vehicles.

In this day of electronic controls, all speed & torque regulation is done in software. It's more than a PID controller (of which the mechanical governors are a vague approximation), with drag torque prediction feedforward control for auxiliary loads & request-&-grant hierarchy for pto loads.

Certainly, my ancient massey with perky engine has all-speed gov. Set the hand throttle to the revs required, drop in the pto & clutch and it will sit there all day at the set speed, unless the gradient gets too steep or the machine jams (ie demanded torque exceeds max available torque at that engine speed)

Hope this helps, David

 

[Steve]

And there was me thinking a tractor was just a tractor.

 

[RF Lighting]

Yeah, but you're a townie

 

[Darkness]

Just came across this little page. Maybe in Canada but interesting to me anyhow. http://www.omafra.gov.on.ca/english/engineer/facts/00-059.htm

 

[stunlawless]

Facinating stuff...

 

[bernardgreen]

Yeah, but you're a townie

Chelsea Tractors have cruise control as standard..... don't they ?